1) Don't shoot weddings. Failing that:
2) Make sure you have extra; Batteries, a backup camera, extra flash, lots of memory cards and someone to help you.
3) If you have a helper, get a reflector he can hold to throw some extra light, especially some warm light. Reflectors have those 5:1 arrangements.
4) FILL IN FLASH, FILL IN FLASH, FILL IN FLASH.. especially, outside! Watch those SHADOWS!!
- what ever you do, don't shoot in the shade without it
5) THE BRIDE is the center piece. The reason for reason... the ONLY important person at the show. Get tons of pictures of her, then her and the groom and then the groom.... and THEN... everyone else.
6) Look at what the PROS shoot. The poses, the backgrounds etc. from inspiration and ideas.
7) I would take a practice run with a friend just to see how your images will turn out on the big day. Know where you are going!
8) Do you need permits?? Shooting in a park? Plan ahead.
9) Make sure you go around and shoot the TABLES when everyone is sitting.
10) You can never take enough pictures. So, take a ton.
11) Get a Gary Fong. They are great flash diffusers.
OK, my very, very limited experience, this is the best I can tell you.
Good luck! Have fun!